Genetic variability in black grouse - What actually is a population?

Conservation measures need to address the quality of both the habitats and of the few surviving specimens of a relict population. Genetic fitness is one of several criteria for assessing the conservation value of surviving individuals. Conservation genetics attempts to preserve the species-specific allelic variation present in populations, and to recognize genetically distinctive populations deserving separate management. Black grouse, on account of the instability of many aspects of their population biology, pose a comparatively serious challenge for these aims ot genetic management : fluctuating population numbers, the polygynous promiscuity of sexually-selected lekking males, and the sometimes strong offspring mortality (probably implying markedly differential survival among clutches), result in strong reproductive variance among individuals. Genetic drift is thus expected to be high, and genetic polymorphisms may rapidly reach fixation by the loss of rare alleles. Rapid evolutionary microevolutionary changes are expected. Fragmentation of habitats and populations might maximize this development. An introductory genetic screening of 95 black grouse (of Central European and Swedish origins), kept and bred for reintroduction at the Institut fur Wildtierforschung (Hannover), provided first arguments that these expectations are actually fulfilled. This cooperative work, performed together with T. Weitzel (Heidelberg) and E. Strauss (Hannover), revealed relatively low allozyme variation over 38 genetic loci. Multi-locus heterozygosity grouped with the lower heterozygosity values published for other lekking grouse species (prairie chickens, sharp-tailed grouse), rather than with heterozygosity estimates on non-lekking tetraonids. Moreover, population hybrids bred from founders derived from different localities in Central Europe produced heavier egg masses than ®pure-bred¯ population lineages from one import locality (E. Srauss). This heterotic increase of egg masses suggests previous genetic lineage divergence. Absolute allozyme-genetic distance among the narrowly founded and questionably population-representative breeding lineages from Bavaria, the Netherlands, or Sweden were slight indeed. Different grouse imported from the same general area in different years differed in certain allelic frequencies. Temporal, short-term stratification of genoytpe frequencies, increasingly observed even in wildlife having a much more stable population biology, might complicate population-genetic work on the necessarily tiny sample sizes from Central European black grouse, if distorted results from inadequate sampling are to be avoided. This hypothesis derived from our less than optimal study material (captive bred grouse, few founders from different origins each) needs confirmation by broader sampling of autochtonous, abundant populations. Model investigations into the temporal stability of genetic marker, frequencies are suggested in such abundant populations, before polymorphic markers can contribute to the genetic management of almost-extinct relict stocks, especially as to their suitability for defining genetically distinctive geographical populations as management units. Based on our experience with genetic screening of other wildlife species, we suggest tile combination of oligo- and polyallellic polymorphic systems to estimate the long-term predictive value of the different marker classes.